Boring or penetrating the earth – Bit or bit element – Rolling cutter bit or rolling cutter bit element
Reexamination Certificate
2000-06-14
2003-08-12
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Rolling cutter bit or rolling cutter bit element
C175S374000
Reexamination Certificate
active
06604587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates generally to roller cone drill bits. Particularly, the invention provides new flat profile cutting element geometries for roller cone bits.
2. Background Art
Roller cone drill bits are commonly used in the oil and gas industry for drilling wells.
FIG. 1
shows one example of a roller cone drill bit used in a conventional drilling system for drilling a well bore in an earth formation. The drilling system includes a drilling rig
10
used to turn a drill string
12
which extends downward into a wellbore
14
. Connected to the end of the drill string
12
is a roller cone-type drill bit
20
.
As shown in
FIG. 2
, roller cone bits
20
typically comprise a bit body
22
having an externally threaded connection at one end
24
, and a plurality of roller cones
26
(usually three as shown) attached at the other end of the bit body
22
and able to rotate with respect to the bit body
22
. Disposed on each of the cones
26
of the bit
20
are a plurality of cutting elements
28
typically arranged in rows about the surface of the cones
26
. The cutting elements
28
can be tungsten carbide inserts, polycrystalline diamond inserts, boron nitride inserts, or milled steel teeth. If the cutting elements
28
are milled steel teeth, the teeth may be coated with a hardfacing material.
Prior art roller cone bits generally have cutting elements arranged so that they contact a formation in an arcuate cross section or “profile.” An example of such a prior art bit is shown in FIG.
3
A.
FIG. 3A
shows a cross section through roller cones
30
of a drill bit
31
. The cross sectional view shows a cutting element profile
36
generated when cross sections of all the cones
30
of the bit
31
are rotated into the same plane. In
FIG. 3A
, the roller cones
30
are rotatably attached to legs
32
of the drill bit
31
. The cutting elements
34
are arranged about the surface of the roller cones
30
. The cutting elements
34
in contact with the bottom of the drilled hole are further illustrated in FIG.
3
B.
FIGS. 3A and 3B
show that prior art bits generally have cutting elements
40
-
43
arranged in an arcuate cutting element profile
36
so that the bit
31
drills a wellbore with a similarly arcuate, rounded bottom hole profile (
38
in FIG.
3
B). The cutting element profile
36
is defined as a curve or line that connects crests
33
of the cutting elements
40
-
43
and that defines the relative shape of the bottom of the hole drilled by the cones
30
. The cutting element profile
36
may be further defined by angular measurements taken at points (such as points A, B, and C in
FIG. 3A
) along the profile
36
. Points A, B, and C are located at midpoints of crests
33
, and angular measurements are defined relative to a horizontal plane (not shown). In
FIG. 3A
, point A is located at the midpoint of a gage cutting element and point C is located at the midpoint of a centerline cutting element. The angular measurements with respect to the horizontal plane at points A, B, and C are 17.5 degrees, 0 degrees, and 14.0 degrees, respectively.
FIG. 3B
shows a planar cross sectional view similar to FIG.
3
A.
FIG. 3B
also shows that the cutting elements of prior art bits typically have crests
44
and
45
that are disposed at various angles with respect to a bit axis of rotation
46
when the cutting elements
40
-
43
are drilling the formation
39
. Therefore, when prior art bits contact the formation with arcuate profiles and at the angles defined by the crests of the cutting elements, the contact between the cutting elements and the formation is generally non-uniform.
BRIEF SUMMARY OF THE INVENTION
The invention is a drill bit that includes a roller cone and a plurality of cutting elements. The roller cone is affixed to a bit body-and is arranged circumferentially about an axis of rotation of the bit.
One aspect of the invention includes cutting elements that are arranged so that the crests of at least half the cutting elements are substantially perpendicular to the bit axis of rotation when the cutting elements are in a downwardmost rotary orientation. In one embodiment, the crests are within about 10 degrees of perpendicular to the axis of rotation. In another embodiment, the crests are within about 5 degrees of perpendicular to the axis. In a particular embodiment, substantially all the crests are within about 10 degrees of perpendicularity to the bit axis.
In another aspect of the invention, the roller cone and the cutting elements are arranged so that the crests on the cutting elements define a substantially flat profile. Substantially flat includes profile angles, with respect to perpendicular to the bit axis, at either the gage edge of the bit or at the bit centerline of 11 degrees or less.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
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Great Britain Search Report, Dated Aug. 7, 2002, 1 page.
Ma Dekun et al., “The Operational Mechanics of The Rock Bit”, Petroleum Industry Press, 1996, pp. 1-243.
Society of Petroleum Engineers Paper No. 29922, “The Computer Simulation of the Interaction Between Roller Bit and Rock”, Dekun Ma, et al, presented Nov. 14-17, 1995, 9 pages.
Society of Petroleum Engineers Paper No. 56439, “Field Investigation of the Effects of Stick-Slip, Lateral, and Whirl Vibrations on Roller Cone Bit Performance”, S. L. Chen et al, presented Oct. 3-6, 1999, 10 pages.
Society of Petroleum Engineers Paper No. 71053, “Development and Application of a New Roller Cone Bit with Optimized Tooth Orientation”, S. L. Chen et al., presented May 21-23, 2001, 15 pages.
Society of Petroleum Engineers Paper No. 71393, “Development and Field Applications of Roller Cone Bits with Balanced Cutting Structure”, S. L. Chen et al., presented Sep. 30-Oct. 3, 2001, 11 pages.
Huang Sujian
Singh Amardeep
Bagnell David
Dougherty Jennifer R.
Rosenthal & Osha L.L.P.
Smith International Inc.
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